Recently, with enhanced integration of semiconductor devices, the wiring density has been increasing and the wiring spacing has been decreasing. This causes an increase of parasitic capacitance of metal wiring, which leads to such problems as RC delay, cross-talk, and increased power consumption. Resultantly, it is imperative to develop a low dielectric material for wiring.
For the insulating material of the conventional IC and LSI semiconductor devices, SiO2 having a dielectric constant of 4.0 is primarily used. In addition, fluorine-doped silicate (F—SiO2), a low dielectric material, is employed in some devices. However, F—SiO2 becomes thermally unstable as the fluorine content increases, so that it is difficult to lower the dielectric constant to below 3.5. Accordingly, a variety of thermally stable organic and inorganic polymers having low polarity are being proposed.
Polyimide resin, polyarylene ether resin, aromatic hydrocarbon resin, and so forth are known as organic polymers having low dielectric constants. These organic polymers have dielectric constants ranging from 3.2 to 2.6. Because of their low glass transition temperatures, they have significantly weaker mechanical strength than SiO2 and very high linear expansion coefficients. Such low thermal stability and elasticity and high linear expansion coefficient may impair reliability of devices or circuit boards.
In order to solve the thermal stability problem of organic polymers, development of organic silicate polymers using alkoxy silane based compounds is in progress. Organic silicate polymers are prepared by hydrolyzing alkoxy silane compounds in organic solvents and condensing the same. Alkoxy silane based compounds such as polymethylsilsesquioxane and polyhydrosilsesquioxane have relatively low dielectric constants of 3.0 or lower, and are thermally stable at 450° C. However, polysilsesquioxane may crack due to shrinkage stress applied in the hardening process, and it has insufficient mechanical strength. In addition, most currently used alkoxysilane based insulating materials have dielectric constants of 2.7 or higher, and it is a long-term objective to reduce the dielectric constant to 2.5 or lower and improve mechanical properties.
As a preparing method of an insulating film having a dielectric constant of 2.5 or lower, a method of preparing organic silicate nanoparticles having large molecular weight by hydrolysis and condensation using a basic catalyst and hardening them to prepare a porous insulating film has been proposed (Japan Patent Publication No. 2001-354903).
Also, a coating composition for insulating film production comprising an organic silicate polymer prepared using an acid catalyst and an organic silicate polymer prepared using a base catalyst has been proposed to improve the mechanical strength of porous insulating film.
However, when an acid catalyst reactant having a small molecular weight is mixed with a base catalyst reactant having a large molecular weight, the dielectric constant may increase abruptly. In particular, because the base catalyst is too reactive, only the acid catalyst is added to improve storage stability. However, when an acid catalyst is added to the base catalyst reactant used in hydrolysis condensation, a salt may be produced, which may cause generation of impurities during long-term storage. To solve this problem, a small amount of water is added to the coating composition for insulating film production to increase solubility of the salt impurities. In this case, the storage stability is improved, but the mechanical strength of the insulating film is not improved at all.
As described above, there have been many attempts to prepare an insulating film having a low dielectric constant and superior mechanical strength and elasticity. However, satisfactory improvement of both the dielectricity and mechanical strength of low dielectric insulating film or super low dielectric porous insulating film for semiconductor devices has not yet been attained.